The employment of electromagnetic actuators for operating the cylinder or gas exchange valves in a piston-type internal combustion engine in place of a mechanical valve control offers the option of a fully variable valve control because of the electronic engine control device required for this. By means of this, it is possible for the first time to take the conditions to be preset, as well as the already set conditions, into account in a very differentiated manner in the course of triggering or controlling the valves.
An electromagnetic actuator for operating a gas exchange valve essentially consists of two electromagnets arranged at a distance from each other, between which an armature acting on the gas exchange valve is guided so it can be moved back and forth against the force of a restoring spring. The two electromagnets are alternatingly supplied with current corresponding to the triggering by the engine control device in such a way that, after the current has been cut off at the respective electromagnet retaining the armature, the latter is moved by the effects of the action of the force of the respective restoring spring in the direction toward the other electromagnet, which will capture it. To overcome the force of the restoring spring at the capturing electromagnet, the latter is supplied with current at an appropriately early time, so that the magnetic force being built up attracts the armature against the force of its restoring spring and brings it to rest against its pole face. Such an actuator represents a spring/mass oscillator constituted by the restoring springs on the one hand and the armature and the gas exchange valve on the other. The energy for initiating the movement of the mass, consisting of the armature and the gas exchange valve, out of the contact position is provided in the form of the spring energy present in the compressed restoring spring, which is released by turning off the current at the retaining electromagnet. The valve now swings almost as far as the opposite end position. The losses occurring during this movement are compensated by supplying current to the capturing magnet and the coupling-in of an electromagnetic capturing energy caused by this when approaching the end position of the capturing electromagnet.
In the course of operating a piston-type internal combustion engine, losses of movement energy occur at the individual spring/mass oscillator systems because of thermodynamic compatibility conditions. For example, the valves, in particular the gas exhaust valves, must be opened against the interior cylinder pressure. This leads to an increased requirement for capturing energy. The system-related stochastic fluctuations of the interior pressure in the combustion chamber lead to changing actual "opening" times of the respective gas exhaust valve, even with the exact control of the time for switching off the current at the retaining magnet of a gas exhaust valve. On the other hand, because of the differing losses during the valve movement in the course of the opening process, a different contacting behavior of the capturing magnet results if a constant capturing energy is coupled in through it.
The operationally caused different contacting behavior of the armature at the capturing magnet then leads to functional and acoustic problems. The stochastic behavior makes it particularly difficult to solve the acoustic problems by means of an optimized minimal capturing energy in connection with an optimal progression of coupling the energy into the magnet systems.